Communication lines use a variety of different components. For example, phone calls can involve cell phone networks, publically switched telephone networks, voice-over-internet protocol, and a wide variety of different hardware. As service providers implement new technologies, the quality of their communication lines may vary.
Further, many communication systems involve mobile components. For example, one end of a phone call may take place on an airplane. The variety and mobility of different aspects of communication systems means that the quality of communication links is affected by variables that are constantly changing and unpredictable.
However, system users such as, for example, businesses or military, may require consistent, quality performance from communication systems. If a particular communication link is not performing up to a certain standard, important commercial or security-related communication may fail. To prevent this, communication customers use service-level agreements to contract for consistent quality service. However, given the global scope and high complexity of communication systems, having a contract in place does not guarantee that communication links will always meet minimum quality standards, such as those set out in SLAs.
Additionally, some communication systems are designed to handle secure communication protocols that require high quality service across a broad bandwidth. In some cases, the inability of a communication line to support secure communication may not be evident. Voice calls may go through without problems even though a line is compromised for security purposes, for example, due to insufficient quality or a breach of security.